1. Field of the Invention
The invention relates to a method of manufacturing a hydrogen-storing alloy based on the Laves phases AB.sub. 2, where A is titanium and/or zirconium, and B is one or more elements from the remaining transition metal series.
2. Discussion of the Background
These hydrogen-storing alloys are composed of intermetallic phases, i.e., chemical compounds of the base components out of which these alloys are made. The stoichiometric ratio of the components are represented adequately by the formula AB.sub. 2, where A is an element at or near the beginning of the transition metal series, and B represents one or more elements from the remainder of the transition metal series. A condition which must be satisfied by A and B is that the ratio of the atomic radii, r.sub.A /r.sub.B, is between 1.05 and 1.68. Such compounds crystallize in the so-called C14 structure, which is distinguished by an especially dense packing of the atoms. The C14, C15, and C36 structures are designated "Laves phase" structures (for intermetallic compounds). The elementary (unit) cell of the C14 structure is hexagonal, having 4 A-atoms and 8 B-atoms. The density of these metallic, very brittle compounds is about 6 g/cm.sup.3.
Numerous examples of such alloys are known from the literature. In addition to titanium and manganese they may be comprised of, preferably, zirconium, chromium, vanadium, iron, cobalt, nickel, copper, and aluminum (in the appropriate combinations). Their "hydrogen storing capacity" is &gt;2 wt. %. (The hydrogen storing capacity is defined as the difference in weight between the hydrogen uptake at room temperature with hydrogen pressure 50 bar and the hydrogen content at 60.degree. C. with a hydrogen pressure of 1 bar, divided by the weight of the storing material.) German OS 30 23 77 discloses examples of such hydrogen-storing alloys, and a method for the molten metallurgical preparation of these alloys i.e., by smelting. In this method, the powdered components of the alloy are mixed together roughly, and then quickly melted in the water-cooled copper crucible of an arc furnace, under vacuum or under a protective gas. The alloy is solidified, comminuted, and remelted in vacuum or under a protective gas, to achieve increased uniformity. These operations may be repeated a number of times.
In order to further improve uniformity, multiple annealing of the hydrogen-storing alloy at 1000.degree. C., under vacuum under a protective gas, has been proposed.
A disadvantage of this known process is that, as a rule, it generally leaves a considerable proportion of oxygen and oxides in the hydrogen-storing alloy. These appreciably reduce storing capacity. Further, it is very costly in terms of labor and energy to manufacture the alloy by repeated melting, cooling, and comminuting, in addition to (possibly) heat treating. Finally, the melting is often accompanied by reactions between the melt and the crucible material, to counteract this, crucible-free melting methods have been proposed, but these are costly.
Accordingly, there is a strongly felt need for a more facile method for the preparation of these alloys. And, ideally, this more facile method should also provide hydrogen-storing alloys with increased hydrogen storing capacity, and not suffer the drawbacks associated with reactions between the melt and the crucible material.